Maternal effects comprise the influences on offspring phenotype resulting from the environmental experience of the mother. An important source of maternal effects is prenatal stress, which can have profound effects on the resulting phenotype of the offspring, and in humans, can lead to impaired growth and serious mental health and physical disorders. Stress results in the secretion of stress hormones that, while beneficial in th short-term, can lead to deterioration in the health of an individual if they remain elevated over a extended period. The particular focus in our proposed studies will be the prenatal maternal stress that ensues when immune responses of females are experimentally induced during reproduction. Our proposed research employs a wild bird model that provides an excellent alternative model to evaluate maternal effects of prenatal stress because: (i) the endocrine systems of birds are similar to those of mammals, (ii) bird embryos are readily amenable to experimental manipulation within eggs, and (iii) wild birds are easily captured and manipulated in their natural environment, allowing inferences about the role of maternal stress to be made in a realistic evolutionary context. Our basic approach for imposing prenatal stress will be to inject females with lipopolysaccharides, a nonliving, nonpathogenic, molecular component of the outer membrane of the cell wall of gram-negative bacteria. Our first aim is to determine whether experimental stimulation of the maternal immune system leads to increased production of the avian stress hormone, corticosterone, that is transferred to the developing embryo in the egg. Aim 2 lies at the heart of the proposed research, with its focus on determining the effects on offspring phenotype of the experimental induction of a stressful prenatal female immune response. Demonstration of such maternal effects as they shape offspring phenotype will provide an unparalleled understanding of how maternal stress is translated into differences in offspring size, health state, and immune function. Finally, our third aim is to determine whether maternal effects arising from prenatal stress can be adaptive, as indicated by beneficial sex-specific effects on offspring fitness. The proposed research will meet a primary goal of the AREA program in that it will expose undergraduate students to research that combines both field and laboratory work in a hypothetico-deductive framework to address important biomedical questions in a natural setting.